How to use rotation with inverse kinematics?

Question

I'm new to Unity, I'm doing a project using inverse kinematics, on one hand (with fingers), and I'm receiving hardware rotation data (quaternion), how to move the fingers of my hand if my only input is rotation , a quaternion on the last finger, and another on the wrist! I'm using the example of the inverse kinematics of Dogzer here the link!

here image of the finger my target is on the distal finger, and I want to claculate the angles of the other fingers using only the ROTATION.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[ExecuteInEditMode]

public class InverseKinematics : MonoBehaviour {  

public Transform upperArm;
public Transform forearm;
public Transform hand;
public Transform elbow;
public Transform target;
[Space(20)]
public Vector3 uppperArm_OffsetRotation;
public Vector3 forearm_OffsetRotation;
public Vector3 hand_OffsetRotation;
[Space(20)]
public bool handMatchesTargetRotation = true;
[Space(20)]
public bool debug;

float angle;
float upperArm_Length;
float forearm_Length;
float arm_Length;
float targetDistance;
float adyacent;

// Use this for initialization
void Start () {

}

// Update is called once per frame
void LateUpdate () {
    if(upperArm != null && forearm != null && hand != null && elbow != null && target != null){
        upperArm.LookAt (target, elbow.position - upperArm.position);
        upperArm.Rotate (uppperArm_OffsetRotation);

        Vector3 cross = Vector3.Cross (elbow.position - upperArm.position, forearm.position - upperArm.position);



        upperArm_Length = Vector3.Distance (upperArm.position, forearm.position);
        forearm_Length =  Vector3.Distance (forearm.position, hand.position);
        arm_Length = upperArm_Length + forearm_Length;
        targetDistance = Vector3.Distance (upperArm.position, target.position);
        targetDistance = Mathf.Min (targetDistance, arm_Length - arm_Length * 0.001f);

        adyacent = ((upperArm_Length * upperArm_Length) - (forearm_Length * forearm_Length) + (targetDistance * targetDistance)) / (2*targetDistance);

        angle = Mathf.Acos (adyacent / upperArm_Length) * Mathf.Rad2Deg;

        upperArm.RotateAround (upperArm.position, cross, -angle);

        forearm.LookAt(target, cross);
        forearm.Rotate (forearm_OffsetRotation);

        if(handMatchesTargetRotation){
            hand.rotation = target.rotation;
            hand.Rotate (hand_OffsetRotation);
        }

        if(debug){
            if (forearm != null && elbow != null) {
                Debug.DrawLine (forearm.position, elbow.position, Color.blue);
            }

            if (upperArm != null && target != null) {
                Debug.DrawLine (upperArm.position, target.position, Color.red);
            }
        }

    }

}

void OnDrawGizmos(){
    if (debug) {
        if(upperArm != null && elbow != null && hand != null && target != null && elbow != null){
            Gizmos.color = Color.gray;
            Gizmos.DrawLine (upperArm.position, forearm.position);
            Gizmos.DrawLine (forearm.position, hand.position);
            Gizmos.color = Color.red;
            Gizmos.DrawLine (upperArm.position, target.position);
            Gizmos.color = Color.blue;
            Gizmos.DrawLine (forearm.position, elbow.position);
        }
    }
  }

}